How to validate in a model, data from a controller

Question

So I have some data that gets pulled from another rails app in a controller lets call it ExampleController and I want to validate it as being there in my model before allowing the wizard to move to its next step and I can't quite figure out how I should be doing it (I know that getting this data directly from the controller into the model violates MVC I am looking for the best workaround to get my data from the controller) . The data must come from the controller as the methods for getting it are contained in ApplicationController however I could do this in the Awizard controller if this is easier. (Also I cannot use a gem)

Please offer some kind of suggestion to the problem and not an explanation of why this is not the correct way to do things I realise that already but cannot do it another way.

---

The Example Controller

should this instead render the data then check it isn't blank elsewhere?

class ExampleController < ApplicationController

  def valid_data?            
    data = #data could be nil or not
    if data.blank?
      return false
    else
      return true
  end

end

---

My Model - (models/awizard.rb)

How do I use the valid_data? method from the example controller? in my validation here.

class AWizard
include ActiveModel::Validations
include ActiveModel::Conversion
include ActiveModel::Dirty
include ActiveModel::Naming

#This class is used to manage the wizard steps using ActiveModel (not ActiveRecord)

attr_accessor :id
attr_writer :current_step  #used to write to current step
define_attribute_methods [:current_step] #used for marking change

validate :first_step_data, :if => lambda { |o| o.current_step == "step1" };

def first_step_data
  #What should i put here to check the valid_data? from the examplecontroller
end

def initialize(attributes = {})
   attributes.each do |name, value|
     send("#{name}=", value)
   end
end

def current_step
  @current_step || steps.first
end

def steps
  %w[step1 step2 step3] #make list of steps (partials)
end

def next_step
  current_step_will_change! #mark changed when moving stepped
  self.current_step = steps[steps.index(current_step)+1] unless last_step?
end

def previous_step
  current_step_will_change! #mark changed when moving stepped
  self.current_step = steps[steps.index(current_step)-1] unless first_step?
end

def first_step?
  current_step == steps.first
end

def last_step?
  current_step == steps.last
end

def all_valid?
  steps.all? do |step|
    self.current_step = step
    valid?
  end
end

def step(val)
  current_step_will_change!
  self.current_step = steps[val]
end

def persisted?
  self.id == 1
end

end

---

Or do I need to add this to this view?

(/views/awizard/_step1.html.erb)

<div class="field">
  <%= f.label 'Step1' %><br />
  #This is the step I want to validate
</div>

---

Answer 1

I maybe have misunderstood the question since my answer is simple. However here's a solution that doesn't resort to metaprogramming, but to the fact that Wizard (the class not objects it creates ) is a singleton/constant.

class ExampleController < ApplicationController

  def valid_data?            
    data = #data could be nil or not
    result = data.blank?
    Awizard.valid_data= result
    result
  end

end

class Wizard
  cattr_accessor :valid_data


  def valid_data?
    self.class.valid_data
  end
end

If course ExampleController#valid_data must have been called before you play around with a Wizard passing step_one.

UPDATE:Reasoning about the global state problem

(raised by @Valery Kvon)

The argument is that Wizard is global to the application and that @wizard instances will be dependant on a global state and are therefore badly encapsulated. But Data, coming from another site, is gloabl in the scope of your app. So there's no mismatch with Wizard beeing the one holding the data. On the contrary it can be considered as a feature.

One example. Wizards magic is only efficient at full moon. Application SkyReport sends data :

:full_moon => true

It affects all wizards in stage 1 if they need to go on step2 of their power. Therefore relying on the global state of Wizard.valid_data? is exactly what we want...

However if each wizard has a personal message coming from Gandalf's application, then we'll want to inforce the invocation of Gandalf's data but then the solution is even simpler :

# in example_controller.rb
before_filter :set_wizard_data, :only => [:create, :update]
....
def set_wizard_data
  @wizard = Wizard.find params[:id]
  @wizard.valid_data= valid_data
end

But this again implies that Gandalf.app knows (something of) the @wizard and from how the problem is presented, data coming from the other site is pretty agnostic !

The issue here is that we don't know enough about the app, its requirements and underlying logic to decide what's good or not...

Answer 2

The only way to share controller level data with model is through external accessor. Using metaprogramming you can trick the way to pass it to a model instance.

controller

def valid_data?            
  data = #data could be nil or not
  result = data.blank? ? false : true
  instance_eval <<-EOV
    def AWizard.new(*args)
      super(*args).tap {|aw| aw.external_valid = #{result}}
    end
  EOV
  result
end

model

class AWizard
  attr_accessor :external_valid

  def initialize(attributes = {})
    attributes.each do |name, value|
      send("#{name}=", value)
    end
  end

  validate :first_step_data, :if => lambda { |o| o.current_step == "step1" };

  def first_step_data
    # :external_valid would be true or false according to a valid_data?. Nil would be if valid_data? has not been called
    if external_valid == false
      errors.add ...
    end
  end
end